I. Field of the Invention
The present invention is directed to a bi-stable electromagnetic operator for a valve. More particularly, the present invention is directed to an electromagnetic device in which a permanent magnet is in close magnetic contact with the core of an electromagnet with the absence of a non-working air gap directly joining the pole ends of the magnet.
II. Discussion of References
U.S. Pat. No. 4,072,918, incorporated by reference, discloses a bi-stable electromagnetic actuator which employs a non-working air gap to maintain a flux path of a predetermined maximum reluctance for a permanent magnet when an armature plate is in a first-stable position. A shunt piece separates the core of an electromagnet from the permanent magnet. The permanent magnet expressly disclosed is made of Alnico V as disclosed at column 5, lines 5-7. Alnico V material has a low coercive force compared to other magnets described below. Because of this low coercive force, the Alnico V material, as well as other ferrite magnets, needs a non-working air gap directly joining the pole ends of the magnet. Furthermore, the permanent magnet of U.S. Pat. No. 4,072,918 needs to be magnetized after assembly of the actuator. This is because the magnet needs to be encased in a highly magnetically permeable steel shell which conducts sufficient magnetic flux lines for the Alnico V material to remain magnetized. Air, not being as magnetically permeable as steel, would not conduct sufficient flux outside the structure. Because Alnico V needs to be magnetized after assembly, one needs a sufficiently strong magnetizer to overcome the tendency of the steel shell to direct the magnetic force of the magnetizer away from the material to be magnetized.
Rare earth-containing magnets of high coercivity have been developed. One example of such is high coercivity rare earth-iron magnets disclosed by U.S. Pat. No. 4,496,395 incorporated herein by reference. The rare earth materials are preferably praseodymium, neodymium and samarium. The magnets include an alloy of the rare earth material and iron. The magnets have higher magnetic coercivity than ferrite magnets. The rare earth-iron magnets have intrinsic room temperature coercivities of at least about 1,000 Oersteds and preferably at least about 5,000 Oersteds. Rare earth-containing magnets are also disclosed by U.S. Pat. Nos. 4,597,938, 4,601,875, 4,601,876, 4,684,406, 4,770,702, 4,770,723, 4,773,950, 4,792,368 which are incorporated herein by reference.